1. Field of the Invention
The present invention relates generally to apparatus for lifting and supporting truck transmissions, gear boxes, and differentials during servicing and repairs, and more particularly, to a truck transmission jack with improved safety and maneuverability.
2. Description of the Relevant Art
Truck transmissions, gear boxes, and differential gear assemblies routinely require servicing. In most cases, such servicing is most efficiently performed by removing the transmission, gear box, or the like, from the truck. Such components typically weigh from 350 to 800 pounds on large trucks, and service personnel require the assistance of a jack to support, lower, and raise, such components in order to remove such components from the truck, and to reinstall such components upon the truck.
Some transmission jacks that are already available are incapable of assuming a low profile near the ground even when collapsed. Such jacks are sometimes difficult to use because they are not easily positioned below the truck, particularly for trucks having low ground clearance. In such cases, the mechanic may actually need to elevate the truck in order to create sufficient ground clearance to insert the jack in position below the truck.
Other transmission jacks that are known may be configured in a relatively compact profile when collapsed, but are incapable of being raised very far off the ground. Such jacks may not have sufficient height to reach the transmission, gear box, or other component to be removed, at least not without inserting wood blocks or other spacers atop the jack and below the component to be removed. However, the need to insert such spacers poses an inconvenience, as well as a safety risk if such spacers shift out of position.
Moreover, many transmission jacks which have been made commercially available, and which have sufficient range of elevation, often become unbalanced and/or unstable when the load is supported at an elevated position. In particular, the load may be supported too close to one end of the jack and tip the jack over or, alternatively, the load may twist or rotate while in an elevated position, potentially causing physical injury to the repairman and further damage to the removed component.
Other transmission jacks which are known to the present applicant typically include hydraulic lifting mechanisms which are built into the transmission jack, often extending horizontally in order to lower the profile of the apparatus. If the hydraulic lifting mechanism fails and can not be repaired, the user must go to the expense of replacing the entire truck transmission jack. Moreover, positioning the hydraulic cylinder horizontally accelerates leakage of hydraulic fluid out of the hydraulic lifting mechanism.
Yet another problem with existing truck transmission jacks is that truck transmissions and gear boxes come in a wide variety of shapes and sizes, yet many existing truck transmission jacks are not easily adjusted to properly support the load in accordance with the particular contour of a specific truck transmission.
Various forms of mobile lifting jacks have been described in previously issued patents. For example, in U.S. Pat. No. 2,621,891 to Marsh, a mobile jack unit is described including a wheeled base, a scissors jack controlled by a threaded draw screw, and a platform for raising and lowering a rear axle differential housing or other load.
U.S. Pat. No. 2,838,278 to Johnsen discloses a transmission jack and a clamping assembly for use therewith in order to adjust for different sizes and makes of transmission housings.
In U.S. Pat. No. 2,940,611 to Burch, an automobile transmission dolly is described for handling truck transmissions. The dolly includes a wheeled base, a pair of lifting arms, a vertical lifting jack for raising the lifting arms, a cradle support, and a cradle for receiving a transmission; a further jacking device is provided for moving the cradle upon the cradle support. The upper end of the vertical jack is coupled to a bridge which is, in turn, coupled to the lifting arms for transmitting a lifting force thereto.
U.S. Pat. No. 2,938,635 to Dyer discloses a wheeled floor jack for removing engines from vehicles. The jack is raised and lowered by operating a handwheel for turning a rotatable screw.
In U.S. Pat. No. 3,109,626 to Arnes et al., a truck transmission jack is described including a tubular base supported by casters. A lifting platform is carried by a pair of lifting beams and a pair of parallel links. A lifting screw is mounted to the base and passes through a nut carried by the lifting beams. A handwheel is operated by the user to turn the lifting screw in order to raise and lower the lifting platform. The lack of hydraulics, and the necessity for turning a handwheel mounted well above the ground make operation of such a device difficult.
U.S. Pat. No. 3,136,526 to Wolf discloses one example of a prior art hydraulic jack mechanism for use under a vehicle to remove transmissions and the like. The Wolf apparatus uses two pairs of support arms which generally extend parallel to one another. However, the apparatus disclosed by Wolf positions the hydraulic piston horizontally; while helping to minimize the profile of the jack when collapsed, the horizontally extending piston and cylinder promote hydraulic fluid leakage. In addition, the Wolf hydraulic ram must be attached at both of its ends to the lifting assembly, making replacement of the hydraulic ram inconvenient. While a handle is provided at one end of the jack assembly, the handle obstructs access to the pump lever of the hydraulic ram. Moreover, the relatively flat, planar platform provided by Wolf to support the transmission is not easily adjusted to support a wide variety of transmissions and other components.
In U.S. Pat. No. 3,559,981 issued to Abshear, an apparatus is shown for removing differentials from vehicles. The apparatus is supported upon a conventional wheeled floor jack.
U.S. Pat. No. 3,958,793 to Garate also discloses a transmission jack for raising and lowering transmissions and the like. A ratchet mechanism prevents the jack from lowering completely to the ground in the event of an inadvertent release of hydraulic pressure. The hydraulic ram is again mounted horizontally, accelerating leakage of hydraulic fluid. In addition, the hydraulic ram requires a mounting block and mounting bolts for being secured horizontally within the apparatus, making replacement of the hydraulic ram more difficult. Like the Wolf jack assembly, the Garate device is provided with a handle at one end of the jack assembly which generally obstructs access to the pump lever of the hydraulic ram. Further, the Garate device uses a pair of chains below the transmission to form a cradle, and a chain which extends over and around the top of the transmission in order to support the transmission, rather than providing rigid supports for positively supporting the underside of the transmission.
U.S. Pat. No. 4,269,394 issued to Gray also discloses a truck transmission jack assembly. Once again, the hydraulic cylinder disclosed by Gray extends horizontally, rather than vertically, and the hydraulic cylinder must be attached to the lifting linkage. No handles are provided as would assist the user in properly positioning the jack assembly below the truck.
In U.S. Pat. No. 4,570,905 to Gerstner, a floor jack assembly for removing auto differentials is disclosed wherein a conventional wheeled floor jack is provided with a platform for supporting differentials. The platform includes a flange which supports a pair of arms each provided with a post adapted to be inserted through a bolt-receiving opening of a differential housing.
U.S. Pat. No. 4,899,985 to Good discloses a castered low profile lift device incorporating a hydraulic bottle jack for raising and lowering a lift head. However, the lift head is raised and lowered by a single lift arm which is subject to lateral sway, as well as tilting at higher elevations.
While many of the jacking devices described above employ pivoting parallelogram structures to maintain the lifting cradle relatively horizontal, the parallel arms which form the parallelogram are typically positioned closely adjacent to one another. Indeed, in many cases, both of the arms forming the parallelogram are pivotally secured to the base at pivot points that are closely adjacent to one end of the base. As the load is raised, the center of gravity of the combined jack and load comes dangerously close to one end of the base. The present applicant has found that greater stability is achieved when the arms forming the pivoting parallelogram are spaced further apart from one another.
Accordingly, it is an object of the present invention to provide a truck transmission jack which is capable of assuming a relatively low profile near the ground when collapsed while being capable of being elevated to an extended height without becoming unbalanced or unstable.
It is another object of the present invention to provide such a truck transmission jack which allows a user to safely and easily support truck transmissions, gear boxes, and the like, without fear that the supported component will twist, rotate, and/or fall off of the jack and injure the user.
It is yet another object of the present invention to provide such a truck transmission jack that is adapted to use a lifting mechanism for raising and lowering the supporting cradle of the jack, wherein the lifting mechanism is easily replaceable at relatively little cost in the event that the hydraulic lifting mechanism should fail.
Still another object of the present invention is to provide such a truck transmission jack which is easily adjusted to fit and safely support the contour of a wide variety truck transmissions, gear boxes, and the like.
A further object of the present invention is to provide such a transmission jack which is capable of supporting and maintaining the load in an elevated position for servicing without maintaining pressure upon the hydraulic lifting system of the jack.
A yet further object of the present invention is to provide such a transmission jack wherein the supporting arms that support the lifting cradle are spaced sufficiently far apart from one another to evenly distribute the weight of the load across the base and to provide a stable support for the lifting cradle.
A still further object of the present invention is to provide such a truck transmission jack which is strong, sturdy, safe, easily operated, and inexpensive to manufacture.
These and other objects of the present invention will become more apparent to those of skill in the art as the description of the present invention proceeds.